Non-reactive Gas Research Articles

Hollow fiber membrane contactor transient experiments for the characterization of gas/liquid thermodynamics and mass transfer properties

We present results from experiments and numerical simulations of contact between a non-reactive gas (N 2O and CO 2) and a physical solvent (H 2O) occurring in a polypropylene (PP) hollow fiber membrane contactor. The closed-loop liquid flow within the experimental setup provides transient curves representing the progressive saturation of the solvent by the gas. We develop an in-house numerical model to fully characterize the gas/liquid mass transfer both in the non-wetted and in the wetted modes, i.e., when the liquid starts partially wetting the pores of the membrane. Using experiments and numerical simulations, we show that the Henry constant ( H) and the molecular diffusion coefficient ( D L A ) of a non-reactive gas absorbing into a liquid solvent can be extracted by parameter estimation. Both parameters are obtained within a single experiment at a constant temperature and the comparison with temperature-dependant correlations yields excellent agreement over the whole range of temperature studied in this work. Simulations show a partial wetting of the membrane pore by the liquid meniscus during a contact between CO 2 and H 2O, possibly due to the plasticizer effect of CO 2 inside the membrane contactor fibers.

Thermodynamics of Non-Reactive Gases Dissolved in Water at Ambient Temperature (T≤333 K): an Update

The thermodynamics of dissolution of non-reactive gases in water under ambient conditions is of importance for the description of the properties of small hydrophobic solutes, and they are also of interest for environmental assessments. The review published in 1977 by Wilhelm, Battino and Wilcock (Chem. Rev. 77:219–262, 1977) constitutes a milestone in this field. However, a number of new data have been published since then, including both solubility and calorimetric determinations. We have analyzed the new data for 27 binary systems reported in the literature at the time of writing this article. Whenever solubility and calorimetric data both exist they have been fitted together. There are, however, systems for which only one type of new thermodynamic information is available; these systems were also analyzed using procedures that are described in this work.

Atomistic phenomena in dense fluid shock waves

The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases.

On Bgk Approximation for Reactive and Nonreactive Flows

In the framework of recently introduced consistent Bhatnagar‐Gross‐Krook (BGK) approximations of the Boltzmann equations for both reactive and nonreactive gas mixtures, the problem of an appropriate choice of relaxation times, which represent the crucial parameters of the model, is addressed. In this first approach, BGK results are tested versus the only exact analytical solutions available in the literature for mixtures, namely the Bobylev‐Krook‐Wu (BKW) modes for space‐homogeneous inert Maxwellian molecules. Results indicate, as expected, that using the actual average collision times in the BGK equations produces a too‐fast dissipation (entropy production) with respect to the Boltzmann description, and that the best fit in that trend is obtained if such times are amplified by a suitable factor, roughly of order two in the cases run.

Thermodynamic analysis of the separation of zinc and lead from electric arc furnace dust by selective reduction with metallic iron

During the remelting of automobile scrap in an electric arc furnace, the contained volatile metals and evolved particulates are captured in the oxidizing off-gas system as a dust. In most countries, this dust is considered as a hazardous waste but contains economically attractive amounts of various non-ferrous metals, such as zinc and lead. One method for recovering these metals is selective reduction, in which the non-ferrous metal oxides are reduced and the metals are simultaneously vaporized and separated, while the iron is maintained in oxide form. In the present research, the utilization of metallic iron as a selective reducing agent was investigated and the equilibrium composition of the reaction products was calculated using the equilibrium module of Outokumpu HSC Chemistry ® 5.1. For the standard conditions, a typical electric arc furnace dust composition was utilized and the temperature was varied from 1273 to 1873 K at atmospheric pressure (1 bar). The zinc and lead recoveries were determined and the separation of the metallic zinc or lead from the iron oxide, was quantified in terms of the selectivity factor ( β). In addition to temperature, the effects of the following variables on the zinc and lead recoveries were determined; reactant ratio (moles of metallic iron per 100 g of dust), dust composition, addition of a non-reactive gas such as nitrogen and also reduced total pressure. The results show that under the appropriate reducing conditions of temperature, reactant ratio and reduced pressure, both high recoveries and selectivity factors can be achieved for both zinc and lead. The calculated results are in reasonable agreement with experimental results, which have been previously published in the literature.

Using dissolved gas analysis to investigate the performance of an organic carbon permeable reactive barrier for the treatment of mine drainage

The strongly reducing nature of permeable reactive barrier (PRB) treatment materials can lead to gas production, potentially resulting in the formation of gas bubbles and ebullition. Degassing in organic C based PRB systems due to the production of gases (primarily CO 2 and CH 4) is investigated using the depletion of naturally occurring non-reactive gases Ar and N 2, to identify, confirm, and quantify chemical and physical processes. Sampling and analysis of dissolved gases were performed at the Nickel Rim Mine Organic Carbon PRB, which was designed for the treatment of groundwater contaminated by low quality mine drainage characterized by slightly acidic pH, and elevated Fe(II) and SO 4 concentrations. A simple 4-gas degassing model was used to analyze the dissolved gas data, and the results indicate that SO 4 reduction is by far the dominant process of organic C consumption within the barrier. The data provided additional information to delineate rates of microbially mediated SO 4 reduction and confirm the presence of slow and fast flow zones within the barrier. Degassing was incorporated into multicomponent reactive transport simulations for the barrier and the simulations were successful in reproducing observed dissolved gas trends.

In situ quantification of methane oxidation in soils using Gas Push–Pull Tests

The Gas Push–Pull Test (GPPT) is a tool for measuring in situ soil processes including methane oxidation. To quantify methane oxidation, methane and non-reactive gases selected based on transport behaviour similar to methane, were injected into soil above a petroleum hydrocarbon contaminated aquifer and gas samples were extracted over time. The rate of loss of methane was compared to the loss of tracer gases and differences in the concentrations were attributed to microbial activity. To further support the evidence for microbial methane consumption, tests were also performed under conditions of inhibited microbial activity.

Impact of chemically enhanced diffusion on dissolved inorganic carbon stable isotopes in a fertilized lake

At high pH the chemical reaction of CO2 with OH− can significantly increase the mass transfer of CO2 between air and water. The reaction of CO2 with OH− strongly fractionates carbon isotopes in comparison to simple diffusion. These processes, chemically enhanced diffusion (CED) and chemically enhanced fractionation (CEF), greatly influence the carbon budgets and carbon isotope ratios for water bodies with high pH. Using floating chambers, we estimated mass transfer coefficients for CO2 and a nonreactive gas, CH4, in an experimentally eutrophied lake. The mass transfer coefficient estimated from CH4 flux did not vary greatly between measurements (k600 = 1.83 ± 0.33 cm h−1; mean ±1 SD) and agreed well with other independent estimates of mass transfer. The mass transfer coefficient of CO2, however, was chemically enhanced by 3.5‐ to 7.5‐fold. This enhancement was related to pH and temperature but was slightly higher than predictions from an existing model. We determined the role of CEF by modifying a model of CED to include both carbon isotopes (12C and 13C). A whole‐lake addition of inorganic 13C to Peter Lake created dynamics in δ13C‐dissolved inorganic carbon (DIC) and provided a test of the new model. The value of δ13C‐DIC decreased from approximately −9‰ to −21‰, a result that was well predicted by the model including CEF but could not be duplicated when CEF was omitted. Thus CED and CEF influenced the mass balance of air‐water CO2 exchange and had isotopic consequences for DIC. Although CEF is considered inconsequential for mean oceanic conditions, this model could be applied to marine systems for inorganic carbon modeling in areas where pH is elevated or physical mass transfer is limited because of low turbulence.

Shock wave interactions with detonable clouds

This paper presents results from the numerical simulation of compressible multi-species gases in an unstructured mesh CFD code called Chinook. Multiple species gases are significant to a wide range of CFD applications that involve chemical reactions, in particular, detonation. The purpose of this paper is to investigate the interaction of shock waves with localized regions of reactive and non-reactive gas species. Test cases are chosen to highlight shock reflection and acceleration through combustion products resulting from the detonation of an explosive charge, and detonation wave propagation through a fuel–air cloud. Computations are performed in a 2D axi-symmetric framework.

Large Eddy Simulation of an Ammonia Jet

A compressible jet flow of ammonia was studied through a series of Large Eddy Simulations. Simulations were focused in the zone where the inertial effects are much bigger than the gravitational ones. The ammonia jet is discharged into an air medium and the gases are treated as a two non-reactive ideal gas mixture. Different simulations were performed, going from the use of constant transport properties to the use of kinetic theory of gases relations for calculating them as a function of the resolved variables. The main goal of the present study is to investigate the effect of varying density as well as variable transport properties on the turbulent flow behavior.

Review and Analysis of Inhalation Dosimetry Methods for Application to Children’s Risk Assessment

Young children have a greater ventilation rate per body weight or pulmonary surface area as compared to adults. The implications of this difference for inhalation dosimetry and children’s risk assessment were evaluated in runs of the U.S. Environmental Protection Agency (U.S. EPA) 1994 reference concentration (RfC) methodology and the ICRP 1994 inhalation dosimetry model. Dosimetry estimates were made for 3-mo-old children and adults for particles and Category 1 and 2 reactive gases in the following respiratory-tract regions: extrathoracic (ET), tracheobronchial (BB), bronchioles (bb), and pulmonary (PU). Systemic dosimetry estimates were made for nonreactive (Category 3) gases. Results suggest similar ET dosimetry for children and adults for all types of inhaled materials. BB dosimetry was also similar across age groups except that the dosimetry of ultrafine particles in this region was twofold greater in 3-mo-old children than in adults. In contrast, the bb region generally showed higher dosimetry of particles and gases in adults than in children. Particle dose in the PU region was two- to fourfold higher in 3-mo-old children, with the greatest child/adult difference occurring for submicron size particles. Particulate dosimetry estimates with the default RfC methodology were below those found with the ICRP model for both adults and children for submicrometer sized particles. There were no cases in which reactive gas dosimetry was substantially greater in the respiratory regions of 3-mo-old children. Estimates of systemic dose of Category 3 gases were greater in 3-mo-old children than in adults, especially for liver dose of metabolite for rapidly metabolized gases. These analyses support the approach of assuming twofold greater inhalation dose in children than adults, although there are cases in which this differential can be greater and others where it can be less.This work was supported by U.S. EPA contract 3W-2915-NATX. The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the state of Connecticut or the U.S. Environmental Protection Agency.

New Field Method: Gas Push−Pull Test for the In-Situ Quantification of Microbial Activities in the Vadose Zone

Quantitative information on microbial processes in the field is important. Here we propose a new field method, the "gas push-pull test" (GPPT) for the in-situ quantification of microbial activities in the vadose zone. To evaluate the new method, we studied microbial methane oxidation above an anaerobic, petroleum-contaminated aquifer. A GPPT consists of the injection of a gas mixture of reactants (e.g., methane, oxygen) and nonreactive tracer gases (e.g., neon, argon) into the vadose zone and the subsequent extraction of the injection gas mixture together with soil air from the same location. Rate constants of gas conversion are calculated from breakthrough curves of extracted reactants and tracers. In agreement with expectations from previously measured gas profiles, we determined first-order rate constants of 0.68 h(-1) at 1.1 m below soil surface and 2.19 h(-1) at 2.7 m, close to the groundwater table. Co-injection of a specific inhibitor (acetylene) for methanotrophs showed that the observed methane consumption was microbially mediated. This was confirmed by increases of stable carbon isotope ratios in methane by up to 42.6 %. In the future, GPPTs should provide useful quantitative information on a range of microbial processes in the vadose zone.

Hollow fiber membrane contactor as a gas–liquid model contactor

Microporous hollow fiber gas–liquid membrane contactors have a fixed and well-defined gas–liquid interfacial area. The liquid flow through the hollow fiber is laminar, thus the liquid side hydrodynamics are well known. This allows the accurate calculation of the fiber side physical mass transfer coefficient from first principles. Moreover, in the case of gas–liquid membrane contactor, the gas–liquid exposure time can be varied easily and independently without disturbing the gas–liquid interfacial area. These features of the hollow fiber membrane contactor make it very suitable as a gas–liquid model contactor and offer numerous advantages over the conventional model contactors. The applicability and the limitations of this novel model contactor for the determination of physico-chemical properties of non-reactive and reactive gas–liquid systems are investigated in the present work. Absorption of CO 2 into water and into aqueous NaOH solutions are chosen as model systems to determine the physico-chemical properties for non-reactive and reactive conditions, respectively. The experimental findings for these systems show that a hollow fiber membrane contactor can be used successfully as a model contactor for the determination of various gas–liquid physico-chemical properties. Moreover, since the membrane contactor facilitates indirect contact between the two phases, the application of hollow fiber model contactor can possibly be extended to liquid–liquid systems and/or heterogeneous catalyzed gas–liquid systems.

Addition of non-reacting gases to the anode flow field of DMFCs leading to improved performance

Contrary to conventional conceptions, we find that an external addition of non-reacting gases to the anode flow field of a direct methanol fuel cell led to improved cell performance. Our theoretical analysis shows that an increase in void fraction of the gas phase in flow channels reduces the cross sectional area of the liquid phase, thereby increasing the liquid velocity. The increased liquid velocity enhances the mass transfer of methanol from the flow channel to the gas diffusion layer and hence, improves cell performance. Following the same idea of accelerating the liquid velocity by reducing channel depth, we further demonstrate experimentally that thinning channel from 3.0 to 0.5 mm resulted in an increase in peak power density by 67.5%.

Effects of the intermixing process between the Lagrangian particles on the estimation of concentration in the Lagrangian particle dispersion model

Abstract A 3-D Lagrangian particle dispersion model, including the photochemical reaction developed by Song et al. (Atmos. Environ. 37 (2003) 4607), has been applied to the data obtained from the Southern Oxidants Study field campaign to examine the effect of the intermixing process between the superposed Lagrangian particles on the spatial distribution of the non-reactive pollutant of SO2 and the photochemical compound of O3 with several different Lagrangian particle releasing time intervals. It is found that the intermixing process tends to disperse the centerline maximum concentration of the non-reactive gas toward the edges of the plume and to enhance the entrainment rate into the plume, thereby reducing the maximum concentration at the center of the plume and widening the width of the plume. The Lagrangian particle releasing time interval of up to 5 min does not significantly affect the non-reactive SO2 concentration across the plume within 49 km (T4 traverse) in the downwind direction from the source. However, a much shorter releasing time interval (an order of minute) is required to simulate the reactive pollutant of O3 concentration compared to the non-reactive SO2 concentration due to excessive entrainment of the background reactive pollutant into the plume center and the overweighed mass of each Lagrangian particle. This result suggests that the present model with the Lagrangian particle releasing time interval of one minute and with the intermixing process between the superposed Lagrangian particles can be used more practically to simulate concentration of both the non-reactive SO2 and the photochemical compound of O3.

Numerical investigation of ${\rm H}_2$ injection in Mach 5 air flow with a strong shock/boundary layer interaction

A numerical study of the hydrogen injection has been investigated in a flow configuration obtained from the interaction of two axisymmetric oblique shock waves produced by a conical ring and a centre-body. This configuration, due to a strong shock/boundary layer interaction, was named a viscous mach interaction (VMI). The geometry which leads to this configuration can be used as a hypersonic inlet, and as this inlet could be axisymmetric or two-dimensional, a first result was to show that this VMI configuration exists in both cases. Different injection locations in the subsonic zone are tested in order to keep this VMI configuration . The influence of the hydrogen injection on the mixing flow behavior is analyzed. The numerical results show that the equivalence ratio \(\Phi\) of the gas-mixture is high enough in order to have a non-reactive gas close to the wall which keeps constant the hydrogen temperature along the centre-body. Thus, the hydrogen injection can play the role of a forward-facing jet reducing heat-transfer at the centre-body wall.

Dynamic surface behaviour of VPO catalysts under reactive and non-reactive gas compositions: an in situ XAS study

The surface of an activated vanadium phosphorus oxide (VPO) catalyst was investigated by means of in situ X-ray absorption spectroscopy in the total electron yield mode. We observed significant changes of the V L3-near edge X-ray absorption fine structure (NEXAFS) when the material was transferred from room temperature to working conditions at 400 °C in the reaction atmosphere. We studied the same VPO material under different gas compositions comprising the reaction mixture of n-butane and oxygen, pure oxygen and vacuum to elucidate the influence of the gas–surface interaction and the effect of the temperature. The results of this extensive study indicate a dynamic response of the catalyst surface to the applied conditions.

Dynamic surface behaviour of VPO catalysts under reactive and non-reactive gas compositions: an in situ XAS study

The surface of an activated vanadium phosphorus oxide (VPO) catalyst was investigated by means of in situ X-ray absorption spectroscopy in the total electron yield mode. We observed significant changes of the V L 3-near edge X-ray absorption fine structure (NEXAFS) when the material was transferred from room temperature to working conditions at 400 °C in the reaction atmosphere. We studied the same VPO material under different gas compositions comprising the reaction mixture of n-butane and oxygen, pure oxygen and vacuum to elucidate the influence of the gas–surface interaction and the effect of the temperature. The results of this extensive study indicate a dynamic response of the catalyst surface to the applied conditions.

Transport of Carbon-14 in a Large Unsaturated Soil Column

Wastes buried at the Radioactive Waste Management Complex (RWMC) of the Idaho National Engineering and Environmental Laboratory (INEEL) include activated metals that release radioactive 14 C as they corrode. To test and refine transport predictions that describe releases to the environment with time, we conducted a series of transport experiments with nonreactive gas- and aqueous-phase tracers and inorganic 14 C species in a large unsaturated soil column filled with sediment representative of that at the RWMC. The tracer tests, hydraulic measurements, and chemical monitoring provided constraints on physical transport parameters, water content, and aqueous–gas partitioning behavior. With those constraints, we estimated a solid–aqueous distribution coefficient for the sediment through inverse modeling of the 14 C transport data, using both a simple gas-diffusion model and a multiphase flow and transport simulator (STOMP). Results indicate that 14 C transport in this system is well described by a reactive gas diffusion model, with a pH-dependent retardation factor. Fitting transport simulations to the early-time transport data yielded K d ≈ 0.5 ± 0.1 mL g −1 , while soil samples removed approximately 1 yr later yielded K d values of 0.8 to 2.4 mL g −1 . These values are consistent with those derived from smaller-scale experiments, demonstrating that laboratory-based measurements provide a valid means of estimating transport behavior at much larger spatial and temporal scales. Assuming that 14 CO 2 migration in the RWMC is dominated by gas transport, our results suggest that most 14 C released from the RWMC would discharge to the atmosphere rather than to the underlying Snake River Plain aquifer.

Transport of Carbon‐14 in a Large Unsaturated Soil Column

Wastes buried at the Radioactive Waste Management Complex (RWMC) of the Idaho National Engineering and Environmental Laboratory (INEEL) include activated metals that release radioactive 14C as they corrode. To test and refine transport predictions that describe releases to the environment with time, we conducted a series of transport experiments with nonreactive gas‐ and aqueous‐phase tracers and inorganic 14C species in a large unsaturated soil column filled with sediment representative of that at the RWMC. The tracer tests, hydraulic measurements, and chemical monitoring provided constraints on physical transport parameters, water content, and aqueous–gas partitioning behavior. With those constraints, we estimated a solid–aqueous distribution coefficient for the sediment through inverse modeling of the 14C transport data, using both a simple gas‐diffusion model and a multiphase flow and transport simulator (STOMP). Results indicate that 14C transport in this system is well described by a reactive gas diffusion model, with a pH‐dependent retardation factor. Fitting transport simulations to the early‐time transport data yielded Kd ≈ 0.5 ± 0.1 mL g−1, while soil samples removed approximately 1 yr later yielded Kd values of 0.8 to 2.4 mL g−1 These values are consistent with those derived from smaller‐scale experiments, demonstrating that laboratory‐based measurements provide a valid means of estimating transport behavior at much larger spatial and temporal scales. Assuming that 14CO2 migration in the RWMC is dominated by gas transport, our results suggest that most 14C released from the RWMC would discharge to the atmosphere rather than to the underlying Snake River Plain aquifer.